In Her Name Dead Soul

In the third book of the In Her Name: The Last War trilogy, three years have passed since the brutal first contact encounter with the alien Kreelan Empire, and the Confederation is desperate for a victory. With over a dozen worlds under siege by legions of Kreelan warriors, President McKenna orders her military leaders to deliver a victory, no matter the cost, to give humanity hope.

Ichiro Sato, his wife Steph, Roland Mills, Scarlet, and the irrepressible General James Sparks are once again at the sharp end of the spear on a mission to take back the colony of Alger's World from the alien invaders before the Kreelans have exterminated the human population.

But overwhelming firepower may not be enough. For leading the Kreelans is Ku'ar-Marekh, a warrior priestess who is feared even among her own kind. With her spirit trapped between life and death, drawn to war from a lonely sojourn among distant stars, she is known by her people as the Dead Soul...
 
If you're new to the In Her Name series, here is the author's recommended reading order:

1. The Last War Trilogy

• First Contact
• Legend Of The Sword
• Dead Soul

2. The Redemption Trilogy

• Empire
• Confederation
• Final Battle

3. The First Empress Trilogy

• From Chaos Born
• Forged In Flame
• Mistress Of The Ages

Note that The Last War and Redemption have also been published as trilogy collections.